The present invention relates to polymeric coating compositions having controllable, reproducible and stable electrical conductivity of, for example, about 1.0 to about 10.sup.-12 S/cm or (ohm-cm).sup.-1. Certain coating compositions with electrical conductivity in the range of about 10.sup.-8 to about 10.sup.-10 S/cm are useful antistatic materials or charge relaxation materials that may be used in electrophotographic image development systems such as liquid image development systems or scavengeless and hybrid scavengeless development systems. The scavengeless development systems do not scavenge or interact with a previously toned image, so as to adversely affect image quality, and are important, for example, in trilevel and highlight color xerography as disclosed, for example, in U.S. Pat. No. 4,078,929. Two-phase conductive compositions contain dispersions of conductive particles, for example, carbon black or graphite, within insulating polymer matrices, for example, dielectric binders such as a phenolic resin or fluoropolyrner, which are close to the percolation threshold concentration. Such concentration levels allow conductive particle contact, resulting in a burst of conductivity, see for example, Brewington et al., U.S. Pat. No. 4,505,573. The dielectric constant of these overcoatings can range from about 3 to about 5, and preferably is about 3. The desired conductivity is achieved by controlling the loading of the conductive particles. However, the low conductivity values required for electrophotographic image development systems and the large, intrinsic electrical conductivity of carbon black make it extremely difficult to achieve predictable and reproducible conductivity values. Very small changes in the loading of conductive particles near the percolation threshold can cause dramatic changes in the coating's conductivity. Furthermore, differences in particle size and shape can cause wide variations in conductivity at even a constant weight loading. Moreover, the percolation threshold approach requires relatively high concentrations of conductive particles. At these concentrations, the coatings tend to become brittle, wherein the mechanical properties becoming controlled by carbon black rather than the polymer matrix.
Another approach to conductive coatings is to molecularly dope a polymer matrix with mixtures of a neutral charge transport molecule and its radical cation or anion. "Molecular doping" refers to the relatively low amounts of dopant added, as compared to carbon black dispersions, to increase the conductivity of the polymer matrix, and suggests that the resulting mixture is essentially a solid solution. No chemical bonding occurs between the dopant and the charge transport molecule so as to produce a new material or alloy. That is, the polymer matrix is rendered mechanically stable with a controlled conductivity by molecular doping with dopants such as oxidizing agents. In the presence of an oxidizing dopant, the partially oxidized charge transport moieties in the charge-transporting polymer act as hole carrier sites, which transport positive charges or "holes through the unoxidized charge transport molecules. As an example, Mort et al., J. Electronic Materials, 9:41 (1980), disdose the possibility of chemically controlling dark conductivity by codoping a polycarbonate with neutral and oxidized species of the same molecule, tri-p-tolylamine, that is, TTA and TTA.sup.+ respectively, where TTA.sup.+ represents a cation radical salt of TTA.
Coating compositions of the present invention have electrical conductivities in the range of about 1.0 to about 10.sup.-10 S/cm and are also useful in various applications such as: thin film transistor devices, see Dodabalapur et al., U.S. Pat. No. 5,574,291, and Tsumura; A. et al., U.S. Pat. No. 5,500,537; in electroluminescent devices, EP 686662-A2, U.S. Pat. Nos. 5,514,878, and 5,609,970, and A. J. Heeger, "Self-assembled Networks of Conducting polyaniline" in Trends in Polymer Science, 3, 39-47, 1995); in liquid crystal displays, U.S. Pat. Nos. 5,619,357 and 5,498,762; in electrochromic devices, U.S. Pat. Nos. 5,500,759, and 5,413,739; in photochromic devices, U.S. Pat. No. 5,604,626; in rechargeable batteries, U.S. Pat. Nos. 4,987,042 and 4,959,430; in secondary cells, U.S. Pat. Nos. 5,462,566 and 5,460,905; in electrochemical capacitors, U.S. Pat. Nos. 5,527,640, 4,910,645, 5,442,197 and 5,626,729; in photovoltaic cells, U.S. Pat. No. 5,482,570; in photodetectors, U.S. Pat. No. 5,523,555; in photosensitive imaging member, U.S. Pat. Nos. 5,616,440 and 5,389,477; in photographic coatings, U.S. Pat. No. 5,443,944; in formation of conductive polymer patterns, U.S. Pat. No. 5,561,030; in electroplating, U.S. Pat. Nos. 5,415,762, 5,575,898 and 5,403,467; in laser applications, Katulin, V. A. et al., Sov. J. Quantum Electron., 14, 74-77 (1984), Hide et al., Science 273, 1833, (1996); and Tessler, et al., Nature, 382, 695 (1996); in polymer grid triodes, U.S. Pat. No. 5,563,424; in anticorrosion coatings, U.S. Pat. Nos. 5,532,025 and 5,441,772; in ferromagnetic or high magnetic spin coatings, Shiomi et al., Synthetic Metals, 85, 1721-1722 (1997), and references cited therein. The disclosures of the aforementioned references are totally incorporated herein by reference.